Senate Judiciary Committee Chairman Lindsey Graham (R-SC) sent a letter to Secretary of State Mike Pompeo on Thursday requesting documents related to Joe Biden’s communications with Ukrainian officials. Graham’s inquiry focuses on any calls Biden may have had with former Ukrainian President Petro Poroshenko about the firing of the country’s top prosecutor, or any calls that referenced Burisma, the Ukrainian gas company where Biden’s son Hunter sat on the board. The Washington Post reports that Graham’s letter appears to begin an investigation into Trump’s widely debunked claim that Biden, who at the time was vice president, put pressure on Ukraine to fire its top prosecutor in an attempt to protect his son. Taylor Reidy, a spokeswoman for Graham, told the Post that the senator is now seeking the documents because “[Rep.] Adam Schiff and the House Intel Committee have made it clear they will not look into the issues about Hunter Biden and Burisma.” “Graham is requesting documents which could shed additional light on that issue and hopes they will be able to answer some of the outstanding questions,” Reidy said.